Nerve tissue that controls the heart's rate of contraction and relaxation; also known as the sinoatrial node. An artificial pacemaker is an electrical device implanted surgically to treat abnormally slow heart rhythms (bradycardias).

PACKED CELL VOLUME (PCV):

A measurement of the volume of red blood cells in relation to the volume of blood fluid, expressed as a percentage; also called the hematocrit.

PALLIATION:

Alleviation of clinical signs in the absence of specific treatment of the underlying disorder.

Any organism that is dependent in some manner for its continued existence on another organism (its host), most often to the detriment of the host.

PARASITEMIA:

Presence of a parasite in the blood circulation.

PARASITOLOGY:

The study of parasites.

PARATENIC HOST:

An "optional" host in a parasite's life cycle in which juvenile stages may persist but do not develop.

PARATHYROID GLANDS:

Twin, small pairs of endocrine glands located adjacent to the thyroid gland; they secrete parathyroid hormone (PTH), which is essential for the regulation of calcium and phosphorus balance in the body.

PARATHYROID HORMONE (PTH):

Hormone secreted by the parathyroid glands that regulates the metabolism of calcium and phosphorus in the body.

PARENTERAL:

By injection (i.e., not by the oral route); injectable.

PARESIS:

Diminished ability to move a muscle or a body part voluntarily.

PARIETAL PLEURA:

Thin transparent membrane that forms the inner lining of the chest cavity.

PAROXYSM:

A sudden bout.

PARROT MOUTH:

Dental malformation consisting of an overshot jaw; actually caused by a shortening of the lower jaw.

PARTURITION:

The act of giving birth.

PASTERN FOLLICULITIS:

The most commonly encountered pus-forming skin infection in the horse, caused by Staphylococcus aureus.

PASTERN JOINT:

The joint between the short pastern bone and the long pastern bone.

PATCH:

A large macule.

PATELLA:

Knee cap, a small triangular sesamoid bone located in front of the knee.

PATELLAR LUXATION:

Congenital displacement of the knee-cap (patella); rare in horses.

PATENT:

Unobstructed, open.

PATENT DUCTUS ARTERIOSUS (PDA):

Abnormal persistence after birth of an embryonic blood vessel connecting the pulmonary artery to the aorta; only rarely seen in horses.

PATENT INFECTION:

With regard to parasites, an infection in a definitive host that results in the appearance of products of the parasite's reproduction (eggs, larvae, etc.).

PATENT URACHUS:

Abnormal persistence of the urachus after birth.

PATHOGEN:

Any microbial agent capable of causing disease.

PATHOGENESIS:

The cellular, biochemical, and pathological mechanism(s) underlying the development of a disease.

PATHOGENIC:

Able to cause disease.

PATHOGENICITY:

The relative ability of an organism to cause disease.

PEDAL OSTEITIS:

Increased vascularization and demineralization affecting the coffin bone, usually secondary to inflammation resulting from repeated, excessive concussion on the sole.

PEDICLE:

A small stalk or stem.

PEDUNCULATED:

Situated on a stalk.

PELVIC FLEXURE:

Area of the large intestine where the intestine narrows and folds back on itself.

PELVIC SYMPHYSIS:

The joint formed by the union of the two halves of the pubic bone of the pelvis.

PELVIS:

Hip.

PEMPHIGUS FOLIACEUS:

Autoimmune skin disease characterized by autoantibody production and the subsequent development of vesicles and pustules in the superficial layers of the skin.

PENICILLINS:

A large group of antibiotics derived primarily from fungi of the genus Penicillium; of pivotal importance in the treatment of diseases caused by certain bacteria such as the streptococci, clostridia, and spirochetes, penicillins interfere with the vital synthesis of bacterial cell walls.

PEPTIDE:

A short chain of amino acids; peptides form the building blocks of proteins.

PEPTIDE HORMONES:

Hormones manufactured by the body from amino acids, sometimes with the addition of carbohydrates (sugars).

PERACUTE:

Of extremely rapid onset.

PERCUTANEOUS NEEDLE BIOPSY:

Technique by which a sample of organ tissue is obtained for examination by maneuvering a biopsy needle through the skin and into the organ of interest.

PERIANAL:

In the region of the anus.

PERICARDIAL EFFUSION:

Abnormal accumulation of fluid in the pericardial sac.

PERICARDITIS:

Inflammation or infection of the pericardium.

PERICARDIUM:

The thin, membranous sac that surrounds the heart, stabilizing its position and protecting it from disease affecting nearby structures.

PERINATAL PERIOD:

The period shortly before and after birth.

PERINEUM:

Region between the thighs encompassing the anus and genitalia.

PERIOCULAR:

Pertaining to the area around the eye.

PERIODIC OPHTHALMIA:

Recurrent inflammation of the eye associated with an abnormal immunologic reaction to leptospires (spiral-shaped bacteria) or threadworms; also known as recurrent uveitis or moon blindness.

PERIODONTAL LIGAMENT:

Structure composed of tiny fibers that serves to attach the tooth root to the bone of the jaw.

PERIORBIT:

Eye socket.

PERIOSTEAL STRIPPING:

The most common surgery for correction of angular limb deformities in foals.

PERIOSTEUM:

The highly sensitive connective tissue sheathing the bones; it contains a rich blood supply and provides for the nutrition, growth, repair, and protection of the underlying bone.

PERIPHERAL NERVOUS SYSTEM (PNS):

The cranial, spinal, and peripheral nerves and their connections to muscle or to sensory receptors.

PERISTALSIS:

Muscular movements of the intestinal tract that function to propel contents longitudinally through the tract.

PERMEABILITY:

Leakiness; ability to be penetrated.

PH:

A measure of the hydrogen ion concentration of a solution, reflective of acidity (pH below 7) or alkalinity (pH above 7), with a pH value of 7 representing neutrality.

An inflammatory condition of the lungs; characterized by the filling of air spaces with fluid, resulting in impaired gas exchange.

PNEUMOTHORAX:

Accumulation of air within the pleural cavity, inside the chest but outside the lungs, impeding the ability of the lungs to expand normally; collapsed lung.

PNEUMOUTERUS:

Accumulation of air inside the uterus; a consequence of pneumovagina.

PNEUMOVAGINA:

Aspiration of air and debris into the vagina; also known as wind-sucking.

POLL:

The back of the head.

POLLAKIURIA:

Increased frequency of urination.

POLYCLONAL GAMMOPATHY:

Increase in serum gamma globulins (blood proteins that include most of the antibody classes) that tends to be spread over a wide range of protein types.

POLYCYTHEMIA:

An excessive number of red blood cells.

POLYDIPSIA:

Excessive thirst.

POLYESTROUS:

Having more than a single estrous cycle per year.

POLYGENIC TRAITS:

Traits that are the result of the action of more than a single gene.

POLYMORPHISM:

Genetic variation.

POLYMORPHONUCLEAR LEUKOCYTE:

Any white blood cell having a lobular nucleus, such as a neutrophil.

POLYNEURITIS:

Inflammation occurring simultaneously in more than one nerve.

POLYP:

A small fleshy mass projecting from the surface of a mucous membrane.

POLYPEPTIDE:

Any peptide containing two or more amino acids; often referred to simply as a peptide.

POLYPHAGIA:

Excessive eating.

POLYSYNOVITIS:

Inflammation of the lining membrane of a joint.

POLYURIA:

Excessive urination.

POSITIVE REINFORCEMENT:

In training, giving a reward such as food for suitable behavior.

POSTERIOR CHAMBER:

That portion of the eye between the iris and the lens.

POSTERIOR PARESIS:

Partial paralysis of either or both hind limbs.

POSTHITIS:

Inflammation of the prepuce.

POSTPARTUM:

Occurring after birth.

POSTPRANDIAL:

Occurring after a meal.

POTOMAC HORSE FEVER:

A gastrointestinal disease of horses, characterized by high fever, colitis (inflammation of the large intestine), diarrhea, and dehydration; caused by a rickettsia, Ehrlichia risticii

POULTICE:

Soft, often medicated paste spread on a cloth and draped over a wound.

PREDILECTION:

Preference.

PREMUNITION:

Maintenance of immunity to a parasite by the persistent presence of small numbers of the parasite, usually in the gastrointestinal tract; premunition immunity wanes if the parasite is completely eliminated from the body.

PREPATENT PERIOD:

The time elapsing between the initiation of a parasite's infection of a definitive host and the appearance of the products of parasite reproduction, e.g., eggs, larvae, etc.

PREPUBERTAL:

Pertaining to the period before sexual maturity.

PREPUCE:

Fold of skin enclosing the penis; also called the sheath.

PRICKLE CELL LAYER:

A layer of cells within the epidermis, the outermost layer of the skin; also known as the squamous cell layer, it lies above the basal cell layer and below the granular cell layer.

PRIMARY HYPERPARATHYROIDISM:

Hyperparathyroidism resulting from excessive, relatively uncontrolled secretion of parathyroid hormone (PTH) by one or more abnormal parathyroid glands.

PRIMARY HYPOPARATHYROIDISM:

Hypoparathyroidism resulting from an absolute or relative deficiency of secretion of parathyroid hormone (PTH).

PRIMARY LYMPHOID ORGANS:

Organs in which the production and maturation of lymphocytes takes place; in horses they include the bone marrow, the mucosal-associated lymphoid tissue (MALT), and the thymus.

PROESTRUS:

In the estrus cycle, the period just before estrus.

PROGESTERONE:

Hormone secreted by the corpus luteum, adrenal cortex, and placenta, whose primary function is to prepare the uterus for pregnancy; also called progestin.

PROGESTOGEN:

Any compound with progesteronelike activity.

PROGLOTTID:

One of the chain of segments comprising the strobila or body of a tapeworm parasite.

PROGNATHISM:

Condition characterized by an elongated lower jaw.

PROGNOSIS:

The outlook for recovery from a disease.

PROLACTIN:

Hormone secreted by the pituitary gland that simulates and sustains lactation; also called lactogenic hormone.

PROLAPSE:

A bulging through or protrusion of a tissue or organ.

PROLIFERATIVE OPTIC NEUROPATHY:

An incidental finding in old horses, consisting of excessive tissue growth in the area of the optic disk (at the back of the eye).

PROPHYLAXIS:

Disease prevention.

PROPTOSIS:

Bulging or protrusion of the eyeball from the eye socket; also called exophthalmos.

PROPULSIVE DIARRHEA:

Squirting, watery diarrhea from the rectum.

PROSTAGLANDINS:

A group of fatty acid-derived compounds that are important as regulators of a number of physiological processes involving allergic reactions, contraction of smooth muscle, dilation of blood vessels, blood clotting, and others.

PROSTATE GLAND:

Gland in male mammals that surrounds the urethra where it joins the bladder and is important in the production of seminal fluid.

PROSTATITIS:

Inflammation of the prostate gland.

PROTEIN-LOSING ENTEROPATHY:

Syndrome occurring in adult horses, characterized by weight loss in the face of a ravenous appetite; the cause is unknown but the result is a "leaky" intestine that does not absorb nutrients properly.

PROTEINS:

Molecules, composed of amino acids, that make up many of the structural components of the body and that are needed to maintain all normal body functions.

PROTEINURIA:

Excessive loss of protein in the urine.

PROTEOLYTIC:

Capable of breaking down protein.

PROTOZOA:

Simple organisms that are usually composed of a single cell; most are free-living but some are capable of producing disease in animals or humans.

PROXIMATE ANALYSIS:

A measure of the nutrient content of a diet, including the maximum moisture, maximum fiber, minimum crude protein, and minimum crude fat content.

PRURITUS:

Itchiness.

PSEUDOHYPERPARATHYROIDISM:

Disorder characterized by elevated levels of blood calcium resulting from production of a parathyroid hormonelike substance by a tumor.

PTYALISM:

Excessive drooling; hypersalivation.

PULMONARY:

Pertaining to the lungs.

PULMONARY EDEMA:

Noninflammatory buildup of fluid in the tissues and air spaces within the lungs.

PULMONARY EMBOLISM:

A detached clot from elsewhere in the body occluding a blood vessel within the lungs.

PULMONIC STENOSIS:

Congenital heart defect characterized by a narrowing (stenosis) of the connection between the right ventricle and the pulmonary artery.

PULMONIC VALVE:

The semilunar valve on the right side of the heart; also called the pulmonic semilunar outflow valve.

PULP:

The blood vessels, nerves, lymphatic channels, and cells that line the pulp chamber or root canal of each tooth.

PUNNETT SQUARE:

Checkerboard diagram for delineating possible outcomes of mating two individuals of defined genotype.

PUPIL:

The central opening of the iris, through which light penetrates into the inner reaches of the eye.

PURPURA HEMORRHAGICA:

Immunologically mediated condition characterized by swelling of the limbs and widespread skin hemorrhages, varying in severity from a mild transient reaction to a severe fatal condition; associated with a number of different inciting factors, occasionally streptococcal infections.

PURULENT:

Pus-forming.

PUS:

Fluid produced by an inflammatory process, containing many white blood cells.

PUSTULE:

A skin vesicle containing pus.

PUTREFACTIVE:

Pertaining to the normal decomposition of organic matter by microorganisms.

PYELONEPHRITIS:

Any infection of the kidney involving as well the renal pelvis.

PYLORIC SPHINCTER:

Sphincter located between the stomach and duodenum.

PYLORUS:

The terminal portion of the stomach, connecting it with the duodenum (first part of the small intestine).

PYODERMA:

General term for any skin disease in which pus is formed.

PYOMETRA:

Accumulation of pus within the uterus, resulting usually from a severe bacterial infection.

PYOMETRITIS:

Purulent inflammation of the uterus.

PYOTHORAX:

Accumulation of pus within the chest; also called thoracic empyema.

PYRROLIZIDINE ALKALOIDS:

Plant toxins that produce a very specific type of liver damage; the most common cause of chronic liver failure in horses in the western United States

Featured Adoptable Horse

ET

ET is a lovely, quiet OTTB who, due to a previous racing injury is unsound. It is possible he will be sound for light riding after a lay up and may make a good trail horse as he is a solid unspooky boy with a great temperament however there is no ... Read More